[edk2-devel] [PATCH v1 05/13] DynamicTablesPkg: Helper function to compute package length
PierreGondois
pierre.gondois at arm.com
Wed Jun 23 11:40:30 UTC 2021
From: Pierre Gondois <Pierre.Gondois at arm.com>
Some AML object have a PkgLen which indicates the size of the
AML object. The package length can be encoded in 1 to 4 bytes.
The bytes used to encode the PkgLen is itself counted in the
PkgLen value. So, if an AML object's size increments/decrements,
the number of bytes used to encode the PkgLen value can itself
increment/decrement.
Therefore, a helper function AmlComputePkgLength() is introduced
to simply computation of the PkgLen.
Signed-off-by: Pierre Gondois <Pierre.Gondois at arm.com>
---
.../Library/Common/AmlLib/AmlEncoding/Aml.c | 87 ++++++++++++++++++-
.../Library/Common/AmlLib/AmlEncoding/Aml.h | 47 +++++++++-
2 files changed, 132 insertions(+), 2 deletions(-)
diff --git a/DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.c b/DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.c
index eadafca97ea5..d829b1869846 100644
--- a/DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.c
+++ b/DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.c
@@ -2,7 +2,7 @@
AML grammar definitions.
Copyright (c) 2010 - 2018, Intel Corporation. All rights reserved. <BR>
- Copyright (c) 2019 - 2020, Arm Limited. All rights reserved.<BR>
+ Copyright (c) 2019 - 2021, Arm Limited. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
@@ -803,3 +803,88 @@ AmlComputePkgLengthWidth (
// Length < 2^6
return 1;
}
+
+/** Given a length, compute the value of a PkgLen.
+
+ In AML, some object have a PkgLen, telling the size of the AML object.
+ It can be encoded in 1 to 4 bytes. The bytes used to encode the PkgLen is
+ itself counted in the PkgLen value.
+ This means that if an AML object sees its size increment/decrement,
+ the number of bytes used to encode the PkgLen value can itself
+ increment/decrement.
+
+ For instance, the AML encoding of a DeviceOp is:
+ DefDevice := DeviceOp PkgLength NameString TermList
+ If:
+ - sizeof (NameString) = 4 (the name is "DEV0" for instance);
+ - sizeof (TermList) = (2^6-6)
+ then the PkgLen is encoded on 1 byte. Indeed, its value is:
+ sizeof (PkgLen) + sizeof (NameString) + sizeof (TermList) =
+ sizeof (PkgLen) + 4 + (2^6-6)
+ So:
+ PkgLen = sizeof (PkgLen) + (2^6-2)
+
+ The input arguments Length and PkgLen represent, for the DefDevice:
+ DefDevice := DeviceOp PkgLength NameString TermList
+ |------Length-----|
+ |--------*PgkLength---------|
+
+ @param [in] Length The length to encode as a PkgLen.
+ Length cannot exceed 2^28 - 4 (4 bytes for the
+ PkgLen encoding).
+ The size of the PkgLen encoding bytes should not be
+ counted in this length value.
+ @param [out] PkgLen If success, contains the value of the PkgLen,
+ ready to encode in the PkgLen format.
+ This value takes into account the size of PkgLen
+ encoding.
+
+ @retval EFI_SUCCESS The function completed successfully.
+ @retval EFI_INVALID_PARAMETER Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlComputePkgLength (
+ IN UINT32 Length,
+ OUT UINT32 * PkgLen
+ )
+{
+ UINT32 PkgLenWidth;
+ UINT32 ReComputedPkgLenWidth;
+
+ if (PkgLen == NULL) {
+ ASSERT (0);
+ return EFI_INVALID_PARAMETER;
+ }
+
+ // Compute the PkgLenWidth.
+ PkgLenWidth = AmlComputePkgLengthWidth (Length);
+ if (PkgLenWidth == 0) {
+ ASSERT (0);
+ return EFI_INVALID_PARAMETER;
+ }
+
+ // Add it to the Length.
+ Length += PkgLenWidth;
+
+ // Check that adding the PkgLenWidth didn't trigger a domino effect,
+ // increasing the encoding width of the PkgLen again.
+ // The PkgLen is encoded in at most 4 bytes. It is possible to increase
+ // the PkgLen width if its encoding is less than 3 bytes.
+ ReComputedPkgLenWidth = AmlComputePkgLengthWidth (Length);
+ if (ReComputedPkgLenWidth != PkgLenWidth) {
+ if ((ReComputedPkgLenWidth != 0) &&
+ (ReComputedPkgLenWidth < 4)) {
+ // No need to recompute the PkgLen since a new threshold cannot
+ // be reached by incrementing the value by one.
+ Length += 1;
+ } else {
+ ASSERT (0);
+ return EFI_INVALID_PARAMETER;
+ }
+ }
+
+ *PkgLen = Length;
+
+ return EFI_SUCCESS;
+}
diff --git a/DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.h b/DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.h
index 35c0680b6159..0641500fcd5f 100644
--- a/DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.h
+++ b/DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.h
@@ -2,7 +2,7 @@
AML grammar definitions.
Copyright (c) 2010 - 2018, Intel Corporation. All rights reserved. <BR>
- Copyright (c) 2019 - 2020, Arm Limited. All rights reserved.<BR>
+ Copyright (c) 2019 - 2021, Arm Limited. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
@@ -326,5 +326,50 @@ AmlComputePkgLengthWidth (
IN UINT32 Length
);
+/** Given a length, compute the value of a PkgLen.
+
+ In AML, some object have a PkgLen, telling the size of the AML object.
+ It can be encoded in 1 to 4 bytes. The bytes used to encode the PkgLen is
+ itself counted in the PkgLen value.
+ This means that if an AML object sees its size increment/decrement,
+ the number of bytes used to encode the PkgLen value can itself
+ increment/decrement.
+
+ For instance, the AML encoding of a DeviceOp is:
+ DefDevice := DeviceOp PkgLength NameString TermList
+ If:
+ - sizeof (NameString) = 4 (the name is "DEV0" for instance);
+ - sizeof (TermList) = (2^6-6)
+ then the PkgLen is encoded on 1 byte. Indeed, its value is:
+ sizeof (PkgLen) + sizeof (NameString) + sizeof (TermList) =
+ sizeof (PkgLen) + 4 + (2^6-6)
+ So:
+ PkgLen = sizeof (PkgLen) + (2^6-2)
+
+ The input arguments Length and PkgLen represent, for the DefDevice:
+ DefDevice := DeviceOp PkgLength NameString TermList
+ |------Length-----|
+ |--------*PgkLength---------|
+
+ @param [in] Length The length to encode as a PkgLen.
+ Length cannot exceed 2^28 - 4 (4 bytes for the
+ PkgLen encoding).
+ The size of the PkgLen encoding bytes should not be
+ counted in this length value.
+ @param [out] PkgLen If success, contains the value of the PkgLen,
+ ready to encode in the PkgLen format.
+ This value takes into account the size of PkgLen
+ encoding.
+
+ @retval EFI_SUCCESS The function completed successfully.
+ @retval EFI_INVALID_PARAMETER Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlComputePkgLength (
+ IN UINT32 Length,
+ OUT UINT32 * PkgLen
+ );
+
#endif // AML_H_
--
2.17.1
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